How Heritability Misleads About Race Ned Block
Total Page：16
File Type：pdf, Size：1020Kb
From The Boston Review, XX, no 6, January, 1996, p. 30-35 How Heritability Misleads about Race Ned Block According to The Bell Curve, Black Americans are genetically inferior to Whites. That’s not the only point in Richard Herrnstein and Charles Murray’s book. They also argue that there is something called "general intelligence” which is measured by IQ tests, socially important, and 60 percent “heritable” within whites. (I'll explain heritability below.) But the claim about genetic inferiority is my target here. It has been subject to wide-ranging criticism since the book was first published last year. Those criticisms, however, have missed its deepest flaws. Indeed, the Herrnstein/Murray argument depends on conceptual confusions that have been tacitly accepted to some degree by many of the book's sharpest critics. Let’s first be clear about the conclusion itself. In a recent article on "The Real Bell Curve," Charles Murray grumbles about critics, such as Stephen Jay Gould, who read the book as saying that racial differences in IQ are mostly genetic. Murray answers by quoting from the book: If the reader is now convinced that either the genetic or environmental explanations have won out to the exclusion of the other, we have not done a sufficiently good job of presenting one side or the other. It seems highly likely to us that both genes and environment have something to do with racial differences. What might the mix be? We are resolutely agnostic on that issue; as far as we can determine, the evidence does not yet justify an estimate (311). In this passage, Herrnstein and Murray are “resolutely agnostic” about whether bad environment or genetic endowment is more responsible for the lower IQs of Blacks. But they indicate no agnosticism at all about whether part of the IQ difference between Blacks and Whites is genetic; and given their way of thinking about the matter, this means that they are not at all agnostic about some Black genetic inferiority. The Simple Argument The Herrnstein-Murray argument for genetic IQ differences is based on two facts: IQ is 60 percent heritable within the White population; and there is a stable, 15-point difference between averages IQs of Whites and Blacks. With IQ largely genetic in Whites, it is natural to conclude — according to Herrnstein and Murray — that the Black-White difference, too, is at least partly genetic. Their argument has more to it; they raise issues about the pattern and the magnitude of the differences that I will get to later. But the most important flaws in the more complex version are fully visible in the simple argument. Herrnstein's and Murray's argument depends on thinking of the 15-point IQ difference as divisible into a genetic chunk and an environmental chunk. This picture suggests the following three alternatives: Extreme Environmentalism: Blacks are genetically on a par with whites, so the IQ gap is all environmental. Extreme Geneticism: Blacks are environmentally on a par with whites, so the IQ gap is all genetic. The Reasonable View: Blacks are worse off both genetically and environmentally: some of the gap is genetic, some environmental. Extreme Environmentalism is thought to be excluded by the 60 percent heritability of IQ. Extreme Geneticism is excluded by well-known environmental effects on IQ together with differences between Black and White environments acknowledged by Herrnstein and Murray. So we are left with The Reasonable View — which postulates some Black genetic inferiority. 1 From The Boston Review, XX, no 6, January, 1996, p. 30-35 Notice, however, that the statement of alternatives blots out a crucial possibility: that Blacks are much worse off than Whites environmentally and better off genetically. Allowing this option, we get a different set of alternatives: genetically, Blacks are worse off — or better off — or equal to Whites. I don't say that it is likely that blacks are better off genetically than whites, but it is possible, and--a very important point--what you consider possible affects what you think is an extremist position. Moreover, the critics of Herrnstein and Murray have tended to trip over this possibility. For example, in a New York Times op-ed critique that describes The Bell Curve as “bogus” and “nothing but a racial epithet,” Bob Herbert insists that “the overwhelming consensus of experts in the field is that environmental conditions account for most of the disparity when the test results of large groups are compared.” In effect, he uses known environmental effects on IQ to argue for a low degree of Black genetic inferiority: in effect, he accepts a version of The Reasonable View. Even Stephen Jay Gould, in his otherwise excellent article in The New Yorker, missteps here. Apparently accepting The Bell Curve's way of conceiving the issue, he complains that Herrnstein and Murray wrongly minimize the large environmental malleability of IQ. He says that they turn “every straw on their side into an oak, while mentioning but downplaying the strong circumstantial case for substantial malleability and little average genetic difference.” Gould does not do enough to guard against the natural interpretation of “little average genetic difference” in the context of discussion of The Bell Curve as little average genetic inferiority of blacks. Several critics in The New Republic (October 31, 1994), in turn, wonder about the size of the “genetic component of the black-white difference,” thereby buying into the same way of thinking. If you accept The Bell Curve’s way of putting the options, then the idea that environmental differences between blacks and whites are big enough to account for 15 IQ points looks like extremism. But given the actual alternatives — that blacks are genetically on a par with whites, or worse off, or better off — zero genetic difference doesn't seem extremist at all. But isn't the idea of Black genetic superiority in IQ a desperate and pathetic attempt to exploit a mere logical possibility? Consider a parallel case. Toe number is genetic in sloths and humans, and humans are observed to have five toes whereas (diurnal) sloths are observed to have three. Is there any real possibility that the genetic toe difference between humans and sloths goes in the opposite direction from the observed toe-number gap? It could be that the three-toed sloth evolved six toes, but we observe only three because of a thalidomide-like chemical which has polluted their food during the years in which we have observed them. But this possibility is only worth mentioning as an example of something extremely unlikely. This example suggests a principle that, though never articulated, underlies all of Herrnstein's and Murray's thinking on genes and IQ: Fundamental Principle: if a characteristic is largely genetic and there is an observed difference in that characteristic between two groups, then there is very likely a genetic difference between the two groups that goes in the same direction as the observed difference. Applying this principle to the case of IQ: given the substantial heritability of IQ, if East Asians are superior in measured IQ, then, according to the Fundamental Principle, they are highly likely to be genetically superior; and if Blacks are inferior in measured IQ, then they are highly likely to be genetically inferior in IQ. But while the Fundamental Principle seems intuitively plausible, it is either irrelevant to the Herrnstein-Murray argument, or simply false. To see the problem, we need first to understand that the term “genetic” has two senses. In the next section, I describe those senses in some detail: to put the point schematically for now, “genetic” can mean either genetically determined or heritable. Once that distinction is in place, the problems for the Principle follow. Again, to put the point schematically for now: if “genetic” is used to mean genetically 2 From The Boston Review, XX, no 6, January, 1996, p. 30-35 determined, then IQ is not genetic, and the Principle is therefore irrelevant. If “genetic” is used to mean heritable, then IQ is genetic but the Principle is false. In neither case, however, does the Principle support the Bell Curve’s claim about genetic differences in IQ. Two Senses of “Genetic” To understand The Bell Curve’s fallacy, we need to distinguish two concepts: the ordinary idea of genetic determination and the scientific concept of heritability, on which all Herrnstein's and Murray's data rely. Genetic determination is a matter of what causes a characteristic: number of toes is genetically determined because our genes cause us to have five toes. Heritability, by contrast, is a matter of what causes differences in a characteristic: heritability of number of toes is a matter of the extent to which genetic differences cause variation in number of toes (that some cats have five toes, and some have six). Heritability is, therefore, defined as a fraction: it is the ratio of genetically caused variation to total variation (including both environmental and genetic variation). Genetic determination, by contrast, is an informal and intuitive notion which lacks quantitative definition, and depends on the idea of a normal environment. A characteristic could be said to be genetically determined if it is coded in and caused by the genes and bound to develop in a normal environment. Consequently, whereas genetic determination in a single person makes sense — my brown hair color is genetically determined — heritability makes sense only relative to a population in which individuals differ from one another — you can't ask “What's the heritability of my IQ?” For example, the number of fingers on a human hand or toes on a human foot is genetically determined: the genes code for five fingers and toes in almost everyone, and five fingers and toes develop in any normal environment.